A problem often encountered in the design and construction of pipe systems is the difficulty of routing inflexible lengths of pipe along paths which change direction. Also, to avoid obstacles in the path of the pipe, it is often necessary to connect pipe sections at angles, complicating the task of connecting the pipes. Further misalignment of the individual pipe sections can make it very difficult to connect them together to complete the system.
Difficulties of connecting pipe sections typically arise in the construction of heating, ventilating, and air conditioning systems for residential and commercial buildings. For example, building codes require that all gas-burning appliances, such as furnaces and water heaters, must be adequately vented so that combustion products are safely channeled outside the building. At the same time, it is desirable to minimize the number of vent pipes extending through the roof or exterior wall of a house or building. Therefore, two or more appliances are often vented through a common exhaust vent. However, the connector pipes which join each appliance to the common vent must be routed around structural members and other obstacles within the building. This causes the connector pipes to meet the common vent pipe at odd angles, making connection to the common vent pipe difficult. Furthermore, because locations of the appliances can vary, as can the location of the common vent and other structures within the building, no two installations are exactly alike.
The situation is further complicated by the increased use of newer, mid-efficiency gas appliances, which have efficiencies of 78 to 83 percent and which are commonly referred to as "fan assisted appliances." With these appliances it is very important to minimize the heat loss through the walls of the vent pipes in order to prevent the formation of excessive condensation within the system. Consequently, many building codes will soon require gas vent systems to be constructed in accordance with "Type B" vent pipe guidelines established by the American National Standards Institute ("ANSI"), Underwriters Laboratories ("UL") and other national and local building codes. To meet ANSI/UL Type B standards, vent pipe must have double walls with an air space between the walls to increase resistance to heat conduction through the pipe. Of course, all connector fittings used in such systems must meet ANSI/UL Type B standards as well.
Previous attempts to solve the problem of connecting misaligned pipes include the use of various combinations of numerous conventional fittings, such as elbows and tees having many different angles and sizes. The fittings are pieced together at the job site in an effort to find the right combination which will complete the connection. However, because the fittings are only available in predetermined angles and sizes, the connections sometimes cannot easily be made. In addition, when the connection is made, the numerous fittings tend to take up an excessive amount of space and can reduce the slope of the connector pipe running from the appliance to the common vent. The reduced slope is a disadvantage because it makes venting less efficient. In addition, the installer is forced to maintain a large stock of fittings for each job.
The prior art discloses various adjustable pipe fittings which are intended to alleviate the pipe connection problem. For example, U.S. Pat. Nos. Re.8,885; 704,936; 1,467,833; 1,708,528; and 1,808,450 disclose adjustable elbow fittings. U.S. Pat. No. 861,409 discloses an adjustable tee fitting designed to accommodate different angular orientations of a branch pipe. U.S. Pat. No. 4,627,646 discloses various types and combinations of adjustable fittings. However, none of these adjustable fittings have the double wall construction necessary to comply with ANSI/UL Type B standards for venting mid-efficiency gas appliances.
Thus, a need exists for a pipe fitting having double walls separated by an air space, as required by ANSI/UL Type B standards, and which is readily adjustable to join two or more connector pipes having various orientations.